Wind and solar power firms are being encouraged to install the generators, which pour out CO2, a greenhouse gas, and toxic nitrogen dioxide, on their sites in order to provide standby generating capacity and prevent the lights going out during periods of peak demand.

The giant Roundponds solar farm, near Melksham, Wiltshire, is among the first green generators to take advantage. The directors of Hive Energy, which owns it, have won permission to put diesel generators near the solar panels — despite local objections.

Similarly, First Renewable has won permission for a diesel farm next to its wind turbines and solar panels at Kettering Energy Park in Northamptonshire.

Diesel generators are typically built into shipping containers, each producing 2-3 megawatts (MW) of power — roughly the same as a large wind turbine. The Department of Energy and Climate Change (Decc) is offering consumer-funded subsidies to firms that install such “short-term operating reserve” because Britain has invested so little in large new power stations that there is a risk of winter power cuts.

Diesel generators are a short-term fix because they can be installed fast and switched on in minutes if needed.

Julian Pertwee, a director at Hive and investor in the Roundponds diesel farm, said: “This is a business opportunity. The country needs standby electricity supplies.”

About 1,000 such diesel units were installed in the past 18 months, with a similar number being planned, making diesel farms among the fastest-growing energy sectors.